Apparatus for continuous production of foamed plastic objects



y 7, 1965 c. R. WILES ETAL 3,196,484

KPPARATUS FOR CONTINUOUS PRODUCTION OF FOAMED PLASTI C OBJECTS Filed Sept. 1. 1961 IN V EN TORS. Char/e6 I?! Wi es Kenn 6/6 R hi/r'on QMQ W I46NT United States Patent 3,196,484 APPARATUS FGR CGNTINUOUS PRODUCTIQN (BF FGAMED PLASTIC QBEECTS Charles R. Wiles, Midland, and Kenneth R. Hilton, Harrison, Mich, assignors to The Dow Chemical Company,

Midland, Mich, a corporation of Delaware Filed Sept. 1, 1961, Ser. No. 135,4% 6 Claims. (Cl. 18-5) This invention relates to an improved apparatus for the forming of expanded thermoplastic resinous articles. It more particularly relates to an apparatus for the continuous forming of particulate expandable thermoplastic material into foamed plastic objects.

Foam plastic bodies are prepared in a variety of manners among which is a method comprising heating an unfoamed or partially foamed particulate mass of organic thermoplastic resinous material confined within a mold to expand the material and cause it to knit together into a coherent unitary object. Various methods are employed to form such bodies such as the methods described in US Patents 2,787,809 and 2,744,291, wherein a particulate mass confined in a mold is immersed in a hot liquid.

Employing these techniques, it is necessary to form each foamed plastic body by What amounts to a repetitive step. Such a step involves employing two mating mold halves, placing an expandable material within the mold cavity, heating the particulate material to expand, fill the mold cavity, and knit together to form a unitary object, subsequently the molded foam objects are cooled, the mold opened and the part removed. Thus, for each object formed, two mold halves are employed and the entire mold assembly must be heated and cooled.

It is an object of this invention to provide an apparatus for the continuous molding of foamed thermoplastic objects from particulate expandable thermoplastic resinous material.

It is still another object of this invention to provide an apparatus for the continuous molding of foamed thermoplastic objects employing molds which form one face of an object and serve to shape the opposite face of a like object.

In accordance with the apparatus of the invention, these objects and other advantages may be attained by providing a first mold having a desired configuration, placing within said desired configuration a quantity of resinous thermoplastic expandable material, placing adjacent said first mold a second mold having a desired configuration, confining said expandable thermoplastic material by means of said first and second molds, adding expandable thermoplastic material to the configuration of said second mold and confining the material therein with a third mold continually sequentially heating said molds and contents thereof to a temperature sufficient to expand the particulate thermoplastic material, sequentially cooling said molds and removing the formed foamed thermoplastic object therefrom.

Also within the scope of the invention is an apparatus for continuously forming foamed thermoplastic objects, said apparatus comprising in cooperative combination a plurality of molds, a housing defining a passage way adapted to receive said molds, said passage way having at least two portions, a heating portion and a cooling portion, said molds being so constructed and arranged that on being placed adjacent to each other in a configuration which may be forced through said passage way a cavity is defined between each of said molds having shape of the object desired to be formed.

Further features, additional advantages, and benefits of the present invention will be more fully manifest in "ice the ensuing description and specification, taken in connection with the accompanying drawing wherein:

FIGURE 1 is a schematic sectional view of an apparatus in accordance with the invention and illustrating the method thereof.

FIGURE 2 is an enlarged representation of a plurality of molds Within the apparatus of FIGURE 1.

FIGURE 3 shows an object formed from expandable thermoplastic resinous material in accordance with the invention.

In FIGURE 1 there is illustrated a schematic cross sectional view of an apparatus in accordance with the invention generally designated by the reference numeral 10. The apparatus 10 comprises a conduit 12 defining a passageway 13. The conduit 12 is comprised of a heating section 14 and a cooling section 15. The heating section 14 is wrapped with an electrical conductor 16 connected to a source of alternating current 18. A plurality of molds 20 are provided which slidably engage the inner surfaces of the passageway 12. A hopper 22 is provided adjacent the uppermost portion of the heating section 14 which also is adapted to slidably engage the molds 20. The mold 20a contains on its inner surface a particulate fomable thermoplastic resin 23. A portion of the resin 23 is also disposed within the hopper 22. The resinous material 23 is contained between the molds 20b and 200 and expanded, substantially filling the void between the molds. The conduit portion 15 is provided with a cooling jacket 25 which is equipped with an inlet 26 and an outlet 27. The space between the conduit portion 15 and the jacket 25 is divided into two portions by diametrically opposed dividers 23 (one shown). A plurality of openings 29 provide communication between passageway 13 and the interior of jacket 25. The cooling portion 15 of the conduit 12 terminates in a mold exit 30.

In FIGURE 2 there is illustrated a schematic cross sectional view of a mating pair of molds, so nested in accordance with the invention as they would appear toward the terminal portion of the heating section 14 of the apparatus of FIGURE 1. The molds 20 are comprised of a magnetic ferrous metal such as iron or steel body section 35 defining a cavity 37, the inner wall of body portion 35 is provided with a non-magnetic conductive liner 38, prepared from metals such as aluminum, copper, and the like, and adjacent the rim of the body portion 35 is a non-magnetic conductive metal sleeve, 39. Disposed between adjacent molds 20 is a thin plastic film liner 42. Surrounding the liner 42 and within the cavity 37 of the mold 20 is a unitary foamed plastic body 43.

FIGURE 3 shows a cutaway view of cup 50 formed in accordance with the invention. The cup 50 comprises a foamed portion 43 rigidly adhered to a liner 42.

In operation of the illustrated embodiment of the invention, the walls of the mold 20 defining the cavity 37 are treated with an adhesive to provide uniform distribution of particulate expandable material. A particulate thermoplastic mass 23 is introduced into the mold in such a manner that the walls thereof are uniformly covered with the expandable particulate plastic. A preformed thin thermoplastic cup liner such as the liner 42 is positioned on the mold 20 opposite the side carrying the expandable thermoplastic material 23. A series of such molds are introduced into the apparatus 10 through the hopper 22 wherein additional granular thermoplastic material 23 is provided to fill the space between adjacent molds. Alternating current is provided to the winding 16 which induces a current in the molds 20. The heating of the molds 20 causes the expandable thermoplastic material between adjacent molds to expand and knit together into a unitary body and bond to'the liner j The molds 20 are advanced through the heating portion 14 into cooling portion where the heat added to the mold by the induction heater is removed and the tached thereto a water supply. Thecoil of copper tubing. was connected to a power source which delivered to the coilabout 300 amperes at'6 volts, 60 cycles altermating" current. The remaining 10 inches of the apparatus was jacketed with a water jacket and provided with means to introduce water into the passageway to assist in cooljingthe molds. The molds were so constructed and ar-' ranged .to' produce a cup which was identical in size with a cup produced by conventional moldingtechniques. The female portion of the'mold was sprayed with about I of a gram of anaqueous solution'consisting of about 50 percent 'commer'cial corn'(Karo) syrup and about /2 percent ef anonionic' detergent "commercially available to prepare the desired objects. Although the molds illustrated have-the form of a cup, a wide variety of other configurations maybe utilized, such as soapdishes, baskets, boxes and the like. Such shapes are readily formed employing mating molds. lvIore intricate shapes are p readily fabricated by employinginserts having appropriate dimensions. I V v Molds for the practiceof the present invention are,

advantageously prepared in accordance'with the teaching of United States Letters Patent. 2,181,874, wherein .in:' duction heater construction and the principles of heating and distributing the heat in a bimetallic body are set forth. Other heating means are readily employedin the practice of the invention such as steam, resistanceheating, and the like. g

The heating means chosen for a particular embodiment will primarilyabe'dependent on "the power sources available and the particular configuration of the object desired. For example, in the continuous manufacture of foam plastic toroids, advantageously, steam, hot gas or liquid circulated throughout a plurality of symmetrical under the trade name Joy.; This solution was uniformly spread over the mold. surface. The cavity was subsequently filled with partly foamed polystyrene beads passing through a 22 mesh sc'reen and retained on a 40 mesh screen. Excess beads'were poured out of the cavity and a uniform layer of beads remainedficoating the'female surface. A cup liner was vacuum formed from a 2 mil-,thickpolystyrene sheet-and was placed over the male portion of the mating mold. ,The liner on the male portion was placed againstthe surface presented by the partly expanded beads adhered to the female 'portionof the mold and the asembled, molds placed in one end of the'heating passageway. Similar sets of molds were coated with partly expanded polystyrene beadsand liners and inserted into theheating passageway forcing the molds already in the passageway toward the cooling section. When the passageway was completely filled with 'molds, those issuing'from the opposite end of the passageway w'ere removed and opened. Well formed cups'were obtained weighing about 2 grams. The'foamed polystyrene was integrallybondedto the polystyrene liner. By way of contrast, cups forinedby themolding of expandable particulate polystyrene by the methods perforatedmoldsis employed. Generally,'xwhen employ- T ing a liquid as aheating medium for the molds and circulating it through the passageway 13, it is generally beneficial to use the heating section onthe bottom and move/the molds in an upward direction, Alternately,

when steam is employed, often it is advantageous to position the, conduit 12in a horizontal direction and pro-' vide openings intermediate between heating section 14 and the cooling section 15 to provide for the escape of;

condensate. Typical expandable ,oftheprior'art weighedS grams. 'cordanee with the' prior 1 art when tested occasionally showed a ,tendency toward. leakage, Notendency to Cups formed in aclealt was observed inithe cups in accordance with the invention: In a similar manner, other expandable particulate polymeric compositions are readily shaped into particulate material'which. may be employed in the practice oftheinventionis described in United States" Letters Patents, 2,744,291 and 2,787,809.'

Commercially,'the most popular of the materials described in these patents are polystyrene beads having 'a' volatile liquid entrapped within, suchas pentane or lowv boiling fluorohalocarbons. g t When thin objects such as cups are. prepared, it -is advantageous to provide a means of distributing a par-J ticulate foamable material uniformly over one and sometimes two surfaces of the mold. This is readily achieved by applying an adhesive to the surface or surfaces of the mold where it is desired to position the expandable material. Suitable adhesives often comprise aqueous starch solutions, solutions of gum'agar, sugar solutions,

a wide variety *of articles including cups, discs, trays,

boxes, stoppers, bungs and ornamental configurations.

fAs is apparent from the foregoing specification, the apparatus of the present invention issusceptible .of being embodied-with various alterations and modifications which may differ particularly from those, that'have been described in. the precedingspecification and description. Forthisreason, it is to be fully understoodthat all of the foregoingis intended to b e'merely illustrative and is not to be construedor interpreted/as being' restrictive and frequently sufiicient adhesion and distribution mayv be attained by wetting the'ysurfaces of the mold with an aqueous solution of detergent or gycerine. 'Whenwater soluble adhesives are employed, they are readily rinsed from the surface of the formed plastic object.

By way of further illustration, a plurality of molds were constructed substantially as shown in FIGURE 2 employing low carbon steel and aluminum havinga diameter of about 3 inches-and designed to form a cup about. 3% inches long and about 2. inchesin-diameter An apparatus comprised a 20 inch long passageway;*a 10 inch portion of one end was, wound with at the base.

58 turns of /1 inch (nominal) copper tubing having ator otherwise limiting of the present invention, excepting as it is set forth and defined in theihereto appended claims.

What is'claimed is: l

of thermoplastic objects from expandable thermoplastic resinous material the apparatus defining a mold passageway adapted to receive molds, the mold passageway having at least a heatingportion and a cooling portion, a

plurality of molds, each of themolds adapted to nest with a like mold' and d'efinea cup-likeconfiguration therebetween," thecup-like'vconfiguration being adapted to receive-expandable thermoplastic resinous material, the housing being generallylvertically disposed, an upwardly opening hopper disposed adjacent the uppermost opening of the mold passageway and the heating portion of the passageway adjacent the hopper.

u 2. The apparatus of claim 1, wherein said heating portion includes aninductionheating means."

'3..The apparatus of claim 2, wherein said molds are adapted to be heated by induction heating.

, 4. The apparatus of claim .2, wherein said molds have a magnetic portion and a non-magnetic conductive portion 1. In a continuous molding appartus for the molding forming a closed loop in a plane normal to the axis of said passageway when inserted in said passage.

5. The apparatus of claim 4, wherein said molds comprise a ferrous metal in thermal contact with a non-ferrous metal. 5

6. An apparatus which continuously forms foamed thermoplastic containers, said apparatus comprising in cooperative combination a plurality of molds,

a housing defining a passageway adapted to receive said molds,

said passageway having a mold entrance and a mold exit,

a supply means adapted to provide particulate expandable thermoplastic material positioned adjacent the mold entrance, said supply means being peripherally disposed about the housing defining the passageway.

an induction coil adapted to provide an alternating electromagnetic field Within the passageway adjacent the supply means,

the housing adjacent the mold exit defining a plurality to pass a cooling fluid from said inlet side to said outlet side through said passageway,

said molds adapted to nest together and define a cuplike configuration therebetween and adapted to receive an expandable thermoplastic resinous material,

each of said molds being comprised of a body of a non-magnetic material having peripheral bands of a magnetic material disposed generally adjacent the thickest portions of the configuration defined by nested molds.

References Cited by the Examiner UNITED STATES PATENTS 1,379,595 5/21 Post.

1,689,584 10/28 Grupe 1848 2,779,062 1/57 Stastny 18-48 2,898,632 8/59 Irwin et a1 1848 2,939,173 6/ 60 Linhorst 18-4 2,959,829 11/60 Brennan 22-75 XR 3,013,304 12/61 Richie et al. 18-42 3,079,639 3/63 Orr 264-51 into an inlet side and an outlet side and adapted 25 WILLIAM J. STEPHENSON, Primary Examiner.

MiCl-IAEL V. BRINDESI, Examiner. 

1. IN A CONTINUOUS MOLDING APPARATUS FOR THE MOLDING OF THERMOPLASTIC OBJECTS FROM EXPANDABLE THERMOPLASTIC RESINOUS MATERIAL THE APPARATUS DEFINING A MOLD PASSAGEWAY ADAPTED TO RECEIVE MOLDS, THE MOLD PASSAGEWAY HAVING AT LEAST A HEATING PORTION AND A COOLING PORTION, A PLURALITY OF MOLDS, EACH OF THE MOLDS ADAPTED TO NEST WITH A LIKE MOLD AND DEFINE A CUP-LIKE CONFIGURATION THEREBETWEEN, THE CUP-LIKE CONFIGURATION BEING ADAPTED TO RECEIVE EXPANDABLE THERMOPLASTIC RESINOUS MATERIAL, THE HOUSING BEING GENERALLY VERTICALLY DISPOSED, AN UPWARDLY OPENING HOPPER DISPOSED ADJACENT THE UPPERMOST OPENING OF THE MOLD PASSAGEWAY AND THE HEATED PORTION OF THE PASSAGEWAY ADJACENT THE HOPPER. 